Roof Design

Aim - For the Given Roof styling, create an ASSEMBLY by developing the essential flanges for the outer roof and creating the reinforcements. As per two calculation methods make calculations to check whether the roof and reinforcement's placements are correct or not.

Given master section -

What is a roof?

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era of horse-drawn carriages, early automobile roofs used similar materials and designs.

Types of roof -

• Convertible roofs
• Roof modules
• Hard tops
• Sunroofs
• T- tops
• Targa tops
• Vinyl roofs

What are reinforcements?

Reinforcements are vertical or inclined components of an enclosed automobile's body that both support its roof and reinforce the torsional rigidity of the body.

Types of reinforcement-

Front roof rail(FR) - The front roof rail provides strength and joins windshield glass, inner panel, and outer body as that portion of the roof needs a stronger hold over these components.

Rear roof rail(RR) - It joins and provides strength to the rear door and the design may differ by the opening approach of the rear door.

Center roof rail - It helps in providing support to the flat area of the roof. As the name goes, it is placed at the center of the roof between the front and rear roof rails.

BOW roof rails - These additional roof rails are included to make more stronger and increase torsional stiffness and load-bearing capacity.

Testing of roof for crashworthiness -

Roof strength evaluations are conducted on a quasi-static test system manufactured by MGA Research Corporation (Figure 3). The system consists of an upright assembly and attached loading head that can be fixed at varying heights from the ground as well as at pitch angles ranging from 5 to +5 degrees to accommodate testing on the driver or passenger side. The roll angle is permanently fixed at 25 degrees. Four hydraulic actuators control the movement of the platen along two linear guides. The entire system is mounted on a T-slot bed plate anchored to the floor of the test facility.

Calculation methods -

1. Heat distortion method - Heat distortion temperature is the temperature at which the metal softens and deforms under a specific load. This study is done to check the ability of the roof to withstand high temperatures with respect to the positioning of the reinforcements which contribute to increased strength.

Why Heat distortion criteria -

• The use of high-tensile steel sheets on car bodies has increased, and the weight of bodies has decreased, to enhance fuel economy.
• by fabricating pieces from thinner sheets. The surface areas of outer panels such as a roof panel and door outers are large, so the effects of weight reduction are also large and thereby the need for thinner panels is high.
• Some studies have noted issues with the outside quality where, when thinner outer panels are employed, the surfaces of shells bend owing to thermal strain during the painting and drying processes in addition to issues with the stamping performance (hence, referred to as thermal distortion).
• The washing, electrodeposition, sealing, and finish coating steps are all included in the painting of a vehicle's body. An automobile body is submerged in an electrocoating solution during the electrodeposition process to create an electrodeposited film.
• The body is then put through the drying process, where hot air from a furnace is used to dry the electrocoating solution. If thermal distortion is discovered, it requires a significant amount of labor -hours for reworking and checks for numerous parts and across multiple manufacturing processes.
• Thermal distortion is frequently evaluated by the exterior check conducted for completed vehicles with various parts installed.
• In countries where the summer is high, there are chances of heat distortion due to sun heat. When the radiation of the sun falls on the form of your car, then due to that heat, thermal expansion occurs, and due to some thermal expansion, the possibility of hanging the roof of the car is higher in that area and the roof of your car becomes weak in that area.
• By this calculation, we verify these things whether your roof will be able to withstand that condition or not.
• If so that the area is not able to tolerate this condition then we have to give better support to that area to make your roof stronger.

formula and judgemental criteria

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [1.10x10^(-3) x l] - 2.68

Judge mental Condition: OK< 2.7

Were,

L =Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

Final result-

2. Snow load prediction method -

• When the snow loads over the roof during winter in snowfall regions. This study will also analyze the roof and whether permanent deformation occurs after removing the snow load. That it may bend but needs to be bounced back to its original position.
• Roof design must pass through these calculations to ensure that it has sufficient stiffness to withstand the load due to the accumulation of snow over the roof.

Prediction criteria -

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where

α = My x Lx2 x 10-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]

Length of Roof panel with the center point between Roof rail Front /Rear as the front and rear reference point.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

Width of the roof panel exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

Roof panel X curvature radius of length s in Side view

The design passed all the criteria of the calculation

Completed design -

Draft analysis -

Conclusion - We developed the roof panel as per the given master section and achieved that and our roof feasibility test that it will perform all the required tests in real life application too.